Air bag gas generating composition

ABSTRACT

A gas-generating composition for air bags, which provides low explosion risk and low toxicity, has at least one gas-generating base selected among urazol and metal salts thereof, as the active ingredient, and an oxidizing agent. Urazol and metal salts thereof can effectively generate gas at a low burning temperature when in combination with the oxidizing agent.

This application is a 371 of PCT/JP96/02760 filed on Sep. 24, 1996.

TECHNICAL FIELD

The present invention relates to an air bag gas generating composition.

The air bag gas generating composition according to the presentinvention possesses advantageous characteristics of suitable burningperformance, low burning temperature, low concentration of toxiccomponents such as CO and NOx in the gas generated by the combustion(hereinafter referred to as "after gas"), and remarkably higher safetythan conventional azide-based gas generating compositions.

BACKGROUND ART

As the requirements concerning driving safety become more rigorous, thedemand for air bag systems is greatly increasing. When a car travellingat high speed is in a crash, the air bag system inflates a nylon bag(air bag) stowed in the steering wheel assembly, the dashboard or thelike to thereby protect the occupants from being injured or killed bythe impact against the interior of the car. The bag is inflated with agas generated by the combustion or decomposition of a gas generatingcomposition held in the system.

The air bag gas generating composition is required to have a number ofperformance characteristics, among which the following four areimportant requirements. First, the gas generating composition shouldhave appropriate burning velocity. For reducing the impact on theoccupants smashing into the air bag, the bag deflates to some extentimmediately after the inflation, releasing part of the gas inside thecar. If the burning velocity is too high, the occupants smash into thebag before deflation, whereas if the burning velocity is low, the bag isnot inflated immediately after the crash. In both cases, the bag can notprotect the occupants. The second requirement is low burningtemperature, i.e., low after gas temperature. High after gas temperaturemay impair the bag and cause the occupants to sustain burns, andmoreover, may burn the bag and cause fire. The third requirement is lowconcentration of toxic components such as CO and NOx in the after gas.If the after gas is high in the concentration of toxic components, theoccupants are likely to be poisoned by the after gas released inside thecar from the deflating bag. The fourth requirement is that the shockignitability (sensitivity to shock ignition) is low. High shockignitability involves a high possibility of explosion or detonation inthe course of production, e.g., in the mixing or molding process, andthus entails a high risk in handling.

Azide-based gas generating compositions comprising sodium azide as thegas generating base, which are generally used at present, show adequateburning velocity and gas temperature, and the gas generated therefrommainly comprises nontoxic nitrogen gas. However, said composition has adrawback of high shock ignitability. Further, since sodium azide used asthe gas generating base causes a fire or toxic fume on decomposition, orforms toxic substances such as sodium oxide and sodium hydroxide onreaction with an oxidizing agent, handling thereof requires constant andclose care, and protection equipment is essential for assuring safety.Moreover, since the absorption of moisture leads to a decrease in theburning performance of sodium azide, there must be a provision for theprevention of moisture absorption. In addition, sodium azide is highlytoxic, and thus it is possible that serious environmental pollution willbe caused by the spread of sodium azide when an air bag-equipped car isfallen into a river or the sea or experiences floods, or when an airbag-equipped car is scrapped with a cutter.

Recently, people have acknowledged the great importance of environmentalprotection and safety of operators and users. The azide-based gasgenerating compositions are not preferred due to the above drawbacks.Accordingly, an azide-free gas generating base substituting for sodiumazide is earnestly demanded to be developed.

Azide-free gas generating bases heretofore proposed includenitrogen-containing organic compounds having an amide group, such asazodicarbonamide of the chemical structural formula H₂ NOCN=NCONH₂(Japanese Unexamined Patent Publications Nos. 32,689/1994, 32,690/1994and 227,884/1994, WO 94/01381, etc.), biscarbamoylhydrazine of thechemical structural formula H₂ NOCHNNHCONH₂ (Japanese Unexamined PatentPublications Nos. 300,383/1995 and 143,388/1996, DE-A-19,516,818 and thelike) and dicyanamide of the chemical structural formula H₂ NC(NH)NHCN(specification of U.S. Pat. No. 4,386,979). In particular, research ismade for the practical use of azodicarbonamide and biscarbamoylhydrazinewhich are generally used as foaming agents for synthetic resins, sincethey are very easily available, inexpensive and remarkably low intoxicity and shock ignitability, and the gas generated by the combustionof these compounds contains very small amount of toxic substances (suchas CO and NOx).

However, there is room for improvement in the thermal decompositionproperties and storage stability of gas generating compositionscomprising azodicarbonamide as a gas generating base. On the other hand,the crystal of biscarbamoylhydrazine have a scale or plate shape, inwhich the binding force between the particles is weak. As a result, gasgenerating compositions comprising biscarbamoylhydrazine as a gasgenerating base have poor moldability, and thus it is difficult to formthe composition into desired pellets. Even if pellets can be formed,they easily disintegrate.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide an air bag gasgenerating composition which is remarkably lower in burning temperature,equivalent or lower in the concentration of toxic components such as COand NOx in the after gas, equivalent in burning velocity, shockignitability, safety, etc., and remarkably lower in explosion risk andtoxicity, compared with the conventional azide-free gas generatingcompositions.

Another object of the present invention is to provide an air bag gasgenerating composition which is remarkably improved in storagestability, good in moldability and free from disintegration of theobtained pellets, compared with conventional azide-free gas generatingcompositions.

Other features of the present invention will become apparent from thefollowing description.

The present invention provides an air bag gas generating compositioncomprising, as active components, at least one gas generating baseselected from urazol or a metal salt thereof, and an oxidizing agent.

The present invention also provides the above air bag gas generatingcomposition further comprising at least one member selected from thegroup consisting of a burning catalyst, a burning control agent and aslagging agent.

The air bag gas generating composition of the present invention isremarkably lower in burning temperature, equivalent or lower in theconcentration of toxic components such as CO and NOx in the after gas,equivalent in burning velocity, shock ignitability, safety, etc., lowerin explosion risk and toxicity, and good in storage stability andmoldability, compared with the conventional azide-free gas generatingcompositions.

Urazol and its metal salts, which are used as the gas generating base inthe air bag gas generating composition of the present invention, havebeen heretofore considered not to have gas generating capability. Thepresent inventors first found that urazol or a metal salt thereof, whenheated in combination with an oxidizing agent, generates nontoxic gas.The present invention has been accomplished based on this finding.

Since urazol and its metal salts have higher heat stability andremarkably higher stability to alkali than azodicarbonamide, use thereofadvantageously broadens the selection range of the oxidizing agent,burning catalyst and the like, and contributes to the significantimprovement in the storage stability of the gas generating compositionof the present invention. Further, unlike biscarbamoylhydrazine, thecrystal form of urazol and its metal salts does not affect themoldability of the gas generating composition. Moreover, urazol and itsmetal salts are very low in toxicity and explosion risk, and thuscontributes to the improvement in the safety of the gas generatingcomposition of the present invention.

The metal salts of urazol are not limited specifically, and include, forexample, alkali metal salts such as potassium salt and sodium salt,alkali earth metal salts such as calcium salt, magnesium salt andstrontium salt. Among them, potassium salt, which is free fromcrystallization water, is particularly preferred.

According to the present invention, at least one gas generating baseselected from urazol or a metal salt thereof is used. It is preferredthat urazol is used in combination with a metal salt thereof. Thecombined use further reduce the concentration of toxic components. Whenurazol is used in combination with a metal salt thereof, they may bemixed before being added. Alternatively, a mixture of urazol and aninorganic salt, an organic salt or the like is formulated into pellets,which are then calcined at usually about 100° C. or more, preferablyabout 120° C. or more for about 0.5 to about several hours, to reacturazol with the inorganic salt, organic or like salt for forming a metalsalt of urazol. Usable inorganic and organic salts are not limitedspecifically and include those known. Inorganic salts of metals areparticularly preferred. Specific examples of the inorganic salts ofmetals are metal carbonates such as potassium carbonate, sodiumcarbonate, calcium carbonate, magnesium carbonate and strontiumcarbonate, metal oxides such as potassium oxide, sodium oxide, calciumoxide, magnesium oxide and strontium oxide, hydroxides such as potassiumhydroxide, sodium hydroxide, calcium hydroxide, magnesium hydroxide andstrontium hydroxide, and the like. When urazol is mixed with a carbonateor a hydroxide of an alkali metal, a metal salt of urazol is formed bymere mixing, without calcining. The inorganic salt and/or organic saltof a metal is used in an amount that does not convert the whole ofurazol into its metal salt.

The inorganic salt of a metal is also used as burning catalyst andburning control agent, as described below. When using the inorganic saltof a metal as burning catalyst or burning control agent, the obtainedpellets are not calcined. However, when using a carbonate or a hydroxideof an alkali metal, it is necessary to use the carbonate or hydroxide ofan alkali metal in an amount larger than the amount that converts thewhole quantity of urazol into an alkali metal salt.

According to the present invention, commercially available urazol andmetal salts thereof can be used as such. The particle size of thesecompounds is not limited specifically, and can be properly selected froma wide range in accordance with, for example, the amount used,proportions to other components such as the oxidizing agent, volume ofthe air bag and other conditions.

The oxidizing agent, another active component of the gas generatingcomposition of the present invention, is not limited specifically andcan be selected from those conventionally used in this field. Preferredare those capable of generating and/or feeding oxygen at hightemperatures, for example, oxohalogen acid salts, nitrates, nitrites,metallic peroxides, hyperoxides, ozone compounds, etc.

Usable oxohalogen acid salts include those known, for example,perhalogenates, halogenates and the like. Examples of perhalogenates arealkali metal salts such as lithium perchlorate, potassium perchlorate,sodium perchlorate, lithium perbromate, potassium perbromate and sodiumperbromate, alkali earth metal salts such as magnesium perchlorate,barium perchlorate, calcium perchlorate, magnesium perbromate, bariumperbromate and calcium perbromate, ammonium salts such as ammoniumperchlorate and ammonium perbromate, and the like. Examples of usefulhalogenates are alkali metal salts such as lithium chlorate, potassiumchlorate, sodium chlorate, lithium bromate, potassium bromate and sodiumbromate, alkali earth metal salts such as magnesium chlorate, bariumchlorate, calcium chlorate, magnesium bromate, barium bromate andcalcium bromate, ammonium salts such as ammonium chlorate and ammoniumbromate, and the like. Among them, alkali metal salts of halogen acidsand perhalogen acids are preferred.

Examples of the nitrate are alkali metal salts such as lithium nitrate,sodium nitrate and potassium nitrate, alkali earth metal salts such asmagnesium nitrate, barium nitrate and strontium nitrate, ammonium saltssuch as ammonium nitrate, and the like. Among them, alkali metal saltsand alkali earth metal salts are preferred, and potassium nitrate andstrontium nitrate are particularly preferred.

Examples of nitrites include alkali metal salts such as lithium nitrite,sodium nitrite and potassium nitrite, alkali earth metal salts such asmagnesium nitrite, barium nitrite and calcium nitrite.

Examples of the hyperoxides include alkali metal compounds such assodium hyperoxide and potassium hyperoxide, alkali earth metal compoundssuch as calcium hyperoxide, strontium hyperoxide and barium hyperoxide,rubidium hyperoxide, cesium hyperoxide and the like.

Examples of the ozone compounds include compounds represented by theformula MO₃ wherein M is a Group Ia element such as Na, Kr Rb, Cs or thelike. In the present invention, metal sulfides such as molybdenumdisulfide, bismuth-containing compounds, lead-containing compounds andthe like can be used as the oxidizing agent.

Among these oxidizing agents, oxohalogen acid salts, nitrates andnitrites are preferred, and oxohalogen acid salts and nitrates areparticularly preferred. They can be used singly or as a mixture of twoor more. Commercially available products of these oxidizing agents canbe used as such, and the shape, particle size and the like are notlimited specifically, and can be properly selected in accordance with,for example, the amount of the oxidizing agent used, proportions toother components, volume of the air bag and other conditions.

The oxidizing agent is used usually in a stoichiometric amountsufficient to completely oxidize and burn the gas generating base,calculated on the basis of the amount of oxygen. The amount of theoxidizing agent can be properly selected from a wide range, since theburning velocity, burning temperature (gas temperature), composition ofthe combustion gas, etc. can be adjusted as desired by suitably changingthe proportions of the gas generating base and oxidizing agent. Forexample, the oxidizing agent is suitably used in a proportion of about10 to about 400 wt. parts, preferably about 100 to about 240 wt. parts,per 100 wt. parts of the gas generating base.

One of the preferred embodiments of the air bag gas generating gascomposition according to the present invention comprises the above gasgenerating base and an oxohalogen acid salt and a nitrate as theoxidizing agent.

The gas generating composition of the present invention may furthercontain, in addition to the above two components, at least one memberselected from the group consisting of a burning catalyst, a burningcontrol agent and a slagging agent.

The burning catalyst is considered to serve mainly to decrease theburning temperature and reduce the concentrations of CO and/or NOx inthe gas. Usable burning catalysts include oxides of the metals of the4th to 6th periods in the periodic table, oxygen-containing metalliccompounds which form said metal oxides when heated, heteropolyacids andthe like.

Specific examples of the oxides of metals of the 4 to 6 periods in theperiodic table are copper oxide, nickel oxide, cobalt oxide, iron oxide,chromium oxide, manganese oxide, zinc oxide, calcium oxide, titaniumoxide, vanadium oxide, cerium oxide, holmium oxide, ytterbium oxide,molybdenum oxide, tungsten oxide, antimony oxide, tin oxide, titaniumoxide and the like. Among them, copper oxide, nickel oxide, cobaltoxide, molybdenum oxide, tungsten oxide, iron oxide, tin oxide, zincoxide and chromium oxide are preferred, and CuO, CoO, NiO, Ni₂ O₃, MoO₃,Cr₂ O₃, TiO₂, SnO, ZnO and Fe₂ O₃ are particularly preferred. Thesemetal oxides include hydrates thereof, for example, hydrates of tungstenoxide, such as WO₃ ·H₂ O. It is preferred that the metal oxide have aBET specific surface area of at least 5 m² /g, more preferably at least10 m ² /g, still more preferably at least 40 m ² /g. Among the abovementioned metal oxides, CuO, MoO, WO₃ and the like have an advantageouscharacteristic of the capability of reducing the CO concentration andNOx concentration at the same time.

The oxygen-containing metal compound which form, when heated, the oxidesof metals of the 4th to 6th periods in the periodic table are notlimited specifically, and those conventionally known can be used. Forexample, oxygen-containing molybdenum compounds which form MoO₃ whenheated include Group VIII metal salts of molybdic acid such as cobaltmolybdate and nickel molybdate, molybdic acid and molybdenum hydroxide,and the like. Oxygen-containing tungsten compounds which form WO₃ whenheated include, for example, tungstic acid, metal salts thereof, and thelike. Examples of the metal salts of tungstic acid include alkali metalsalts such as lithium tungstate, potassium tungstate and sodiumtungstate, alkali earth metal salts such as calcium tungstate andmagnesium tungstate, Group VIII metal salts of tungstic acid such ascobalt tungstate, nickel tungstate, iron tungstate and copper tungstate.

Examples of heteropolyacids include phosphomolybdic acid,phosphotungstic acid, metal salts of these acids, and the like. Themetal salts of heteropolyacids are not limited specifically and includeGroup VIII metal salts such as Co salt, Ni salt and Fe salt, Mg salt, Srsalt, Pb salt, Bi salt, etc. Among them, Group VIII metal salts arepreferred, and Co salt is particularly preferred.

Among the above burning catalysts, CuO, CoO, NiO, Ni₂ O₃, MoO₃, WO₃,oxygen-containing molybdenum compounds which form MoO₃ when heated,oxygen-containing tungsten compounds which form WO₃ when heated, cobaltphosphomolybdate, Cr₂ ₃, TiO₂, SnO, ZnO, Fe₂ O₃, etc. are particularlypreferred, and CoO, NiO, Ni₂ O₃, MoO₃, WO₃, Group VIII metal salts ofmolybdic acid, cobalt phosphomolybdate and the like, etc. are still morepreferred.

These burning catalysts can be used singly or as a mixture of two ormore.

The particle size of the burning catalyst is not limited specifically,and can be properly selected from a wide range in accordance with, forexample, the amount of the burning catalyst used, proportions to theother components, volume of the air bag and other conditions. The amountof the burning catalyst is not limited specifically, and can be properlyselected in accordance with, for example, the kinds and proportions ofthe other components, volume of the air bag and other conditions. It issuitable to use the burning catalyst in an amount of usually about 0.1to about 150 wt. parts, preferably about 0.5 to about 80 wt. parts, morepreferably about 5 to about 30 wt. parts per 100 wt. parts of the totalamount of the gas generating base and oxidizing agent.

When using the oxygen-containing metal compound which forms a metaloxide when heated, it is used in an amount that forms the abovespecified amount of metal oxide.

The burning control agent is used generally to decrease the burningtemperature, to control the burning velocity and to prevent the gasgenerating agent from detonation caused by fire or strong impact in thecourse of production, transportation or storage.

The following (a) to (i), for example, can be used as the burningcontrol agent.

(a) Powders of metals such as B, Al, Mg, Ti, Zr, Mo, etc.

(b) Oxides, hydroxides, carbonates and bicarbonates of elements of the3rd period in the periodic table such as B, Al, Mg, Si, etc.(preferably, B₂ O₃, aluminum hydroxide, bentonite, alumina, diatomaceousearth, silicon dioxide, etc.)

(c) Carbonates, bicarbonates, oxides and hydroxide of alkali metals suchas Na, K, etc.

(d) Carbonates, bicarbonates and hydroxides of alkali earth metals suchas Ca, Mg, Ba, Sr, etc.

(e) Chlorides, carbonates, sulfates and hydroxides of elements of the4th to 6th periods in the periodic table other than those mentioned inthe above (b) and (c) (for example, Zn, Cu, Fe, Pb, Ti, V, Ce, Ho, Ca,Yb, etc.)

(f) Cellulose compounds such as carboxymethyl cellulose, hydroxymethylcellulose, their ethers, microcrystalline cellulose powders, etc.

(g) Organic polymeric compounds such as soluble starch, polyvinylalcohol, partially saponified products thereof, etc.

(h) Organic acids such as organic carboxylic acid, for example, aminoacids (e.g., glycine), ascorbic acid, citric acid, etc.

(i) Derivatives of boric acid such as H₃ BO₃, HBO₂, etc.

Among the above burning control agents, substances (a) to (d) and (h)and (i) are preferred, and powders of metals such as B, Al, Ti and Z,metal oxides such as B₂ O₃ and Al₂ O₃, carbonates of alkali metals andalkali earth metals such as lithium carbonate and calcium carbonate,metal hydroxides such as aluminum hydroxides, amino acids such asglycine and derivatives of boric acid are particularly preferred.

These burning control agents can be used singly or as a mixture of twoor more. Commercially available products of these burning control agentsmay be used as such. The particle size thereof is not limitedspecifically, and can be properly selected from a wide range inaccordance with, for example, the amount of the burning control agentused, proportions to the other components, volume of the air bag andother conditions.

The amount of the burning control agent is not limited specifically, andcan be properly selected from a wide range in accordance with theproportions to the other components, volume of the air bag and otherconditions. It is suitable, however, to use the burning control agent inan amount of usually about 0.1 to about 50 wt. parts, preferably about0.5 to about 30 wt. parts per 100 wt. parts of the total amount of thegas generating base and the oxidizing agent.

The slagging agent is an additive which solidifies the residue of thecombustion of the gas generating agent, and thereby facilitates theremoval of the residue with the filter in the air bag inflator. Knownslagging agents are usable, which include, for example, silicon dioxideand alumina mentioned above as the burning control agent, boron oxide(in particular B₂ O₃), etc. These slagging agents can be used singly oras a mixture of two or more. The amount of the slagging agent is notlimited specifically, and can be properly selected from a wide range inaccordance with the formulation of the gas generating composition andother conditions. For example, when silicon dioxide is used as theslagging agent, the molar ratio of the slagging agent to the potassiumnitrate is preferably about 1/2. Also usable as the slagging agent areoxides containing alkali earth metals and alkali earth metal compoundswhich form oxides by reaction, for example, strontium oxide, strontiumnitrate and the like.

Various additives conventionally used in this field and variousadditives used in azide-free gas generating compositions can be furtheradded in a range which does not adversely affect the advantageouscharacteristics of the gas generating composition of the presentinvention.

The following compositions (a) and (b) are preferred gas generatingcompositions of the present invention.

(a) A gas generating composition comprising the gas generating base ofthe present invention, an oxidizing agent, a burning catalyst and aslagging agent. Particularly preferred oxidizing agents are potassiumperchlorate, potassium nitrate, mixtures of these compounds, and thelike. Preferred burning catalysts are copper oxide, nickel oxide,molybdenum oxide and the like. Preferred slagging agent are silicondioxide and the like.

(b) A gas generating composition comprising the gas generating base ofthe present invention, an oxidizing agent, a burning control agent and aslagging agent. Preferred oxidizing agents are potassium perchlorate,nitrate, mixtures of these compounds, and the like. Preferred burningcontrol agents include carbonates of alkali earth metals such as calciumcarbonate, and the like. Preferred slagging agents are silicon dioxideand the like.

According to the present invention, the gas generating base and/or theoxidizing agent, and optionally other additives, may be surface-treatedfor further improving the storage stability, facility of preparation andthe like of the gas generating composition.

Known surface treating agents are usable which include, for example,coupling agents, inorganic surface-treating agents, and the like.Chelating agents can also be used as the surface treating agent.

The coupling agent is not limited specifically and includes thoseconventionally known. Examples are silane-based coupling agents such asγ-aminopropyl-triethoxysilane, γ-glycidyloxypropyltrimethoxysilane andmethyltrimethoxysilane, titanate-based coupling agents such asisopropyltriisostearoyl titanate, aluminum-based coupling agents such asacetoalkoxyaluminum diisopropylate. Usable inorganic surface treatingagents also include those known, among which water-soluble metal saltsare preferred. Examples of the water-soluble metal salts are chloridessuch as AlCl₃, CoCl₂, ZrCl₄, SnCl₂, SnCl₄, TiCl₃, TiCl₄, FeCl₂, FeCl₃,CuCl₂, NiCl₂ and MoCl₅, nitrates of metals such as Al, Co, Zr, Sn, Ti,Fe, Cu, Ni and Mo, silicates such as Na₄ SiO₄ and K₂ Si₄ O₉, ZrCl₂ O,NaAlO₂ and the like. Among them, AlCl₃, NaAlO₂, FeCl₂ and FeCl₃ arepreferred, and NaAlO₂ is particularly preferred. Known chelating agentsare also usable. Examples are ethylenediamine tetraacetic acid (EDTA)and metal salts thereof (EDTA·disodium salt, EDTA·dipotassium salt,EDTA·dilithium salt, EDTA·diammonium salt, etc.), sodiumdiethyldithiocarbamate and the like.

These surface treating agents can be used singly or as a mixture of twoor more. The amount of the surface treating agent is not limitedspecifically, and can be properly selected from a wide range inaccordance with the kinds and proportions of the components to betreated, such as the gas generating base, oxidizing agent and othercomponents, the kind of the surface treating agent, desired performancecharacteristics of the resulting gas generating composition and otherconditions. It is suitable, however, to use the surface treating agentin a proportion of about 0.01 to 5 wt. %, preferably 0.1 to 2.0 wt. %,based on the total amount of the components to be treated.

The surface treatment can be carried out by a conventional processcomprising mixing the component to be treated and the surface treatingagent.

When a water-soluble metal salt is used as the surface treating agent, acomponent can be surface-treated by mixing the component and thewater-soluble metal salt in water, neutralizing the mixture andfractionating and drying the resulting solids. The pH adjustor used forneutralization is not limited specifically, and may be a known acid oralkali. Examples of the acid are inorganic acids such as hydrochloricacid, sulfuric acid, oxalic acid, nitric acid and phosphoric acid,organic acids such as acetic acid, and the like. Examples of the alkaliare sodium hydroxide, potassium hydroxide, sodium carbonate, potassiumcarbonate, sodium hydrocarbonate, potassium hydrocarbonate, ammonia,etc. The treated component is dried usually at about 0° to about 250°C., preferably about 50° to about 150° C., taking into consideration theheat decomposition temperature of said component. The drying is carriedout usually under normal pressure, but may be done under reducedpressure. The gas generating base may be finely ground or recrystallizedbefore being surface-treated.

The gas generating composition of the present invention is produced bymixing the gas generating base, the oxidizing agent and other optionalcomponents.

The gas generating composition of the present invention can be preparedinto a suitable shape. For example, a suitable amount of a binder ismixed with the gas generating composition of the present invention, andthe mixture is tabletted and optionally dried. For the preparation, asolvent such as water or warm water is preferably added in a suitableamount to assure safety. Useful binders include, for example, thoseusually used for this purpose. The shape of the preparation is notcritical and includes, for example, pellets, disks, balls, bars, hollowcylinders, confetti and tetrapods. It may be solid or porous (e.g.honeycomb-shaped). One or more projections may be formed on one or bothsurfaces of pellets or disks. The shape of projections is not limitedspecifically and includes, for example, cylinders, cones, polygonalcones, polygonal pillars, etc.

Alternatively, the respective components may be individually made into apreparation and the preparations may be used as mixed.

The preparation of the gas generating preparation of the presentinvention is placed into a container made of polyethylene or likesynthetic resin or metal, whereby the gas generating preparation can besafely stored and transported.

The air bag gas generating composition of the present invention is notlimited to automotive use and can be suitably used as a gas source forair bag systems to be installed in various transport means.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention is described below in more detail with referenceto the following Examples, Comparative Examples and Test Examples. Themanufacturers of the starting materials used in these examples are asfollows unless otherwise specified. Urazol: product of Otsuka Kagaku K.K. Azodicarbonamide: product of Otsuka Kagaku K. K.Biscarbamoylhydrazine: product of Otsuka Kagaku K. K. Potassium nitrate:product of Otsuka Kagaku K. K. Potassium perchlorate: product of NihonCarlit Co., Ltd. Silicon dioxide: trade name "Nipseal NS-P", product ofNippon Silica Co., Ltd. Soluble starch: Wako 1st grade product, productof Wako Pure Chemical Industries, Ltd. Copper oxide: specific surfacearea 48 m² /g, average particle size about 7.4 μm, product of NikkiChemical Co. Ltd. Molybdenum oxide (VI): product of Nippon InorganicColour & Chemical Co., Ltd.

In the following description, part(s) and percentage are all by weight.

EXAMPLE 1

Thoroughly mixed together were powders of 45 parts of urazol, 57.8 partsof potassium perchlorate, 10 parts of copper oxide (II) and 1 part ofsilicon dioxide. A 20% aqueous solution of soluble starch was added inan amount that gives a starch content of 1.5 parts, and the mixture wasfurther stirred to give a wet powder. The wet powder was granulatedusing a granulating machine. The obtained wet granules were dried andcompressed using a hydraulic tablet molding machine to give a pelletsample of a gas generating composition (6 mm in diameter, 3 mm inthickness and 0.15 g in weight).

Comparative Example 1

Thoroughly mixed together were powders of 45 parts of azodicarbonamide,53.6 parts of potassium perchlorate, 10 parts of potassium nitrate, 1part of silicon dioxide and 3 parts of molybdenum oxide (VI). A 20%aqueous solution of soluble starch was added in an amount that gives astarch content of 1.5 parts, and the mixture was further stirred to givea wet powder. The wet powder was granulated using a granulating machine.The obtained granules were dried and compressed using a tablet moldingmachine to give a pellet sample of a gas generating composition (6 mm indiameter, 3 mm in thickness and 0.15 g in weight).

Comparative Example 2

Thoroughly mixed together were powders of 45 parts ofbiscarbamoylhydrazine, 72.1 parts of potassium perchlorate, 10 parts ofpotassium nitrate, 1 part of silicon dioxide and 5 parts of molybdenumoxide (VI). A 20% aqueous solution of soluble starch was added in anamount that gives a starch content of 3.5 parts, and the mixture wasfurther stirred to give a wet powder. The wet powder was granulatedusing a granulating machine. The obtained granules were dried andcompressed using a tablet molding machine to give a pellet sample of agas generating composition (6 mm in diameter, 3 mm in thickness and 0.15g in weight).

Test Example 1

40 g each of the pellet samples of the gas generating compositionsobtained in Example 1 and Comparative Examples 1 and 2 was individuallyfilled into a 0.3 mm-thick aluminum cup, and the cup was placed in thecombustion chamber of an inflator having a gas outlet 7 mm in diameterand loaded with 0.8 g of boron/potassium nitrate as a transfer charge.The inflator was set in a 60-liter tank and actuated by applying thecurrent, to thereby ignite the pellet sample of the gas generatingcomposition. Then, the pressure and temperature in the inflator and the60-liter tank were measured. After the burning, the gas in the 60-litertank was collected into a 1-liter tedlar bag and checked for the CO andNOx concentrations using a detector tube. The results are shown in Table1.

The symbols in Table 1 stand for the following.

CP max: maximum pressure (kgf/cm²) in the combustion chamber of theinflator

TP max: maximum pressure (kgf/cm²) in the 60-liter tank, a parameter ofthe gas generating capability of the gas generating composition

tTP max: time (msec) in which the internal pressure of the 60-liter tankreaches the maximum, a parameter simulating the velocity of theinflation of the air bag

tTP 90: time (msec) in which the internal pressure of the 60-liter tankreaches 90% of the maximum, a parameter simulating the velocity of theinflation of the air bag

                  TABLE 1                                                         ______________________________________                                                             Comp.   Comp.                                                         Ex. 1   Ex.1    Ex.2                                             ______________________________________                                        CP max (Kgf/cm.sup.2)                                                                        170       170     102                                          TP max (kgf/cm.sup.2)                                                                        1.5       1.8     1.2                                          tTP max (msec.)                                                                              47        30      28                                           tTP 90 (msec.) 21        16      17                                           Tank temperature (°C.)                                                                87        150     75                                           CO concentration (%)                                                                         0.63      0.64    0.48                                         NOx concentration (ppm)                                                                      1050      1050    1200                                         ______________________________________                                    

Table 1 reveals that the gas generating composition of the presentinvention exhibits equivalent burning velocity and is equivalently lowin the concentration of toxic components such as CO and NOx in the aftergas of the composition, compared with the gas generating compositioncomprising azodicarbonamide or biscarbamoylhydrazine as an activecomponent.

Test Example 2

The burning temperature of the gas generating compositions of Example 1and Comparative Examples 1 and 2 was calculated by a simulation based ona thermal equilibrium calculation program of NASA (S. Gordon and B. J.McBride, "A Computer Program for Complex Chemical EquilibriumCompositions-Incident and Reflected Shocks and Chapian JouguetDetonations, NASA). The burning temperatures of the gas generatingcomposition of Example 1, Comparative Example 1 and Comparative Example2 were about 2200K (pressure: 70 kgf), about 2400K (pressure: 70 kgf)and about 2150K (pressure: 70 kgf), respectively.

As apparent from the above, the burning temperature of the gasgenerating composition of the present invention is lower by about 200Kthan that of the gas generating composition comprising azodicarbonamideas the gas generating base.

Further, it was revealed that the gas generating composition of thepresent invention shows burning temperature equivalent to that of thegas generating composition comprising biscarbamoylhydrazine as the gasgenerating base.

Test Example 3

The pellet sample of the gas generating composition obtained in Example1 was stored in a constant temperature vessel at 107° C. for 400 hours.The remaining proportion (wt. %) was calculated to determine the degreeof decomposition of the gas generating base. The remaining proportion ofthe gas generating composition of Example 1 was at least 99.5%, whichproves that urazol substantially did not decompose. The remainingproportion (wt. %) of the pellet sample of the gas generatingcomposition of Comparative Example 1 was determined in the same manneras above with the exception that the storing time was 190 hours, andfound to be 75%. It was proved that azodicarbonamide considerablydecomposed, even in less than half of the storing time of the pelletsample of the gas generating composition according to the presentinvention.

It is apparent from these results that the gas generating composition ofthe present invention is much higher in storage stability than the gasgenerating composition comprising azodicarbonamide as the gas generatingbase.

Test Example 4

Each of the pellet samples of the gas generating compositions obtainedin Example 1 and Comparative Example 2 was set on a hardness tester(trade name "HARDNESS TESTER KHT-20N", product of Fujiwara Seisakusho K.K.) wherein the load (kg) on the pellet was gradually increased, and theload at which the pellet disintegrated was regarded as the hardness ofthe pellet. The hardness test was repeated several times to calculatethe average value. The results are shown in Table 2.

                  TABLE 2                                                         ______________________________________                                                    Number of                                                                              Hardness of                                                          determinations                                                                         pellet (kg)                                              ______________________________________                                        Example. 1    20         8.0                                                  Comp.Ex.2     20         2.8                                                  ______________________________________                                    

It is apparent from Table 2 that the gas generating composition of thepresent invention has remarkably good moldability and high pelletstrength, compared with the biscarbamoylhydrazine-based gas generatingcomposition.

EXAMPLE 2

Thoroughly mixed together were powders of 45 parts of the gas generatingbase, 1 part of silicon dioxide, and potassium perchlorate and aninorganic salt of a metal in the amounts (part) shown in Table 3. A 20%aqueous solution of soluble starch was added in an amount that gives astarch content of 1.5 parts, and the mixture was further stirred to givea wet powder. The powder was granulated using a granulating machine, andthe obtained wet granules were dried and compressed using a hydraulictablet molding machine to give a pellet sample of an air bag gasgenerating composition of the present invention (6 mm in diameter, 3 mmin thickness and 0.15 g in weight).

                  TABLE 3                                                         ______________________________________                                        Amount of         Inorganic salt of metal                                             KClO.sub.4             Amount                                         No.     (part)        Kind     (part)                                         ______________________________________                                        1       62.20         CaCO.sub.3                                                                             20                                             2       62.15         CaCO.sub.3                                                                             30                                             3       62.15         MgCO.sub.3                                                                             18.8                                           4       62.15         SrCO.sub.3                                                                             32.9                                           5       62.15         Mg(OH).sub.2                                                                            6.5                                           6       50.10         K.sub.2 CO.sub.3                                                                       31                                             ______________________________________                                    

The pellet samples Nos. 1 to 5 of the gas generating compositions wereheated at 120° C. for 2 hours to form a metal salt of urazol. The pelletsample No. 6, which contains K₂ CO₃ as the inorganic salt of a metal,was not heated.

The pellet samples Nos. 1 to 6 were tested for burning performance inthe same manner as in Test Example 1. The theoretical burningtemperature of these gas generating compositions was calculated in thesame manner as in Test Example 2. The results are shown in Table 4.

                  TABLE 4                                                         ______________________________________                                        No.         1      2       3    4     5    6                                  ______________________________________                                        Amount of pellet                                                                          40     40      40   40    40   40                                 sample (g)                                                                    CP max (Kgf/cm.sup.2)                                                                     116    128     156  226   136  100                                TP max (kgf/cm.sup.2)                                                                     0.8    0.5     1.7  2.4   1.8  0.8                                Tank temperature                                                                          54     60      178  225   243  --                                 (°C.)                                                                  CO concentration                                                                          0.48   0.61    0.27 0.13  0.32 0.65                               (%)                                                                           NOx         1500   1500    500  1450  850  1500                               concentration                                                                 (ppm)                                                                         Theoretical 2090   2030    2050 2090  2150 1970                               burning                                                                       temperature (K.)                                                              ______________________________________                                    

EXAMPLE 3

No.7: Thoroughly mixed together were powders of 45 parts of urazol,52.05 parts of potassium perchlorate, 20 parts of potassium carbonateand 9 parts of silicon dioxide. A 20% aqueous solution of soluble starchwas added in an amount that gives a starch content of 1.5 parts, and themixture was further stirred to give a wet powder. The wet powder wasgranulated using a granulating machine, and the obtained wet granuleswere dried and compressed using a hydraulic tablet molding machine togive a pellet sample of the bag gas generating composition of thepresent invention (6 mm in diameter, 3 mm in thickness and 0.15 g inweight).

No.8: A pellet sample (6 mm in diameter, 3 mm in thickness and 0.15 g inweight) of the gas generating composition of the present invention wasprepared in the same manner as in the preparation of the pellet sampleNo. 7 with the exception that the amounts of potassium perchlorate andsilicon dioxide were changed to 54.95 wt. parts and 15 parts,respectively.

The pellet samples Nos. 7 and 8 of the gas generating compositions ofthe present invention were tested for burning performance in the same asin Test Example 1. The theoretical burning temperature of these gasgenerating compositions were calculated in the same manner as in TestExample 2. The results are shown in Table 5.

                  TABLE 5                                                         ______________________________________                                        No.                  7      8                                                 ______________________________________                                        Amount of pellet sample (g)                                                                        40     40                                                CP max (Kgf/cm.sup.2)                                                                              98     136                                               TP max (kgf/cm.sup.2)                                                                              1.4    1.4                                               Tank temperature (°C.)                                                                      243    154                                               CO concentration (%) 0.58   0.29                                              NOx concentration (ppm)                                                                            650    1050                                              Theoretical burning  1990   2000                                              temperature (K.)                                                              ______________________________________                                    

We claim:
 1. An air bag gas generating composition comprising, as activecompounds, as least one gas generating base selected from the groupconsisting of urazole and a metal salt thereof, and an oxidizing agentselected from the group consisting of oxohalogen acid salts nitrites,metallic peroxides hyperoxides and ozone compounds.
 2. An air bag gasgenerating composition comprising, as active compounds, as least one gasgenerating base selected from the group consisting of urazole and ametal salt thereof, an oxidizing agent selected from the groupconsisting of oxohalogen acid salts, nitrites, metallic peroxideshyperoxides and ozone compounds, and at least one member selected fromthe group consisting of a burning catalyst, a burning control agent anda slagging agent.
 3. An air bag gas generating composition according toclaim 1 or 2 wherein said at least one gas generating base is a mixtureof urazole and a metal salt thereof.
 4. An air bag gas generatingcomposition according to claim 1 or 2 wherein the oxidizing agent is anoxohalogen acid.
 5. An air bag gas generating composition comprising, asactive compounds, a gas generating base consisting of urazole and ametal salt thereof, and an oxidizing agent.
 6. An air bag gas generatingcomposition according to claim 5, wherein said metal salt is selectedfrom the group consisting of alkali metal salts, and alkali earth metalsalts.
 7. An air bag gas generating composition comprising, as activecompounds, a gas generating base consisting of urazole and a metal saltthereof, an oxidizing agent, and at least one member selected from thegroup consisting of a burning catalyst, a burning control agent and aslagging agent.
 8. An air bag gas generating composition according toclaim 7, wherein said metal salt is selected from the group consistingof alkali metal salts, and alkali earth metal salts.